In physics, the term supersaturation or oversaturation refers to a solution that contains more of the dissolved material than could be dissolved by the solvent under existing circumstances. It can also refer to a vapor of a compound that has a higher (partial) pressure than the vapor pressure of that compound. Small particles (seeds) can trigger the separation of the dissolved material from the solvent or condensation of the vapor. In the solid form these seeds can lead to the formation of crystallites or even large single crystals.
Supersaturated solutions are prepared or result when some condition of a saturated solution is changed, for example temperature, volume (as by evaporation), or pressure.
Carbonated water and beer are examples of supersaturated solutions of carbon dioxide gas in water. At the elevated pressure in the bottle, water can dissolve more carbon dioxide than at atmospheric pressure. At atmospheric pressure, the carbon dioxide gas escapes very slowly from the supersaturated liquid. This process is accelerated by the presence of seeds, such as small bubbles, caused by shaking the bottle, or another solute, such as sugar powder. In air that is supersaturated with water, water droplets may precipitate upon being disturbed. This can be observed in a cloud chamber. In the more general context a cloud may form.